1. Technical Field
The present disclosure relates to a semiconductor structure, and more particularly, to a semiconductor light-emitting structure having low thermal stress.
2. Description of Related Art
As new type light source, LEDs are widely used in various applications. An LED includes an LED chip to emit light. A conventional LED chip includes a substrate, and an N-type semiconductor layer, a light-emitting layer and a P-type semiconductor layer sequentially grown on the substrate. The substrate is generally made of sapphire (Al2O3) for providing growing environment to the layers. However, such a sapphire substrate has a low heat conductivity, causing that heat generated by the layers cannot be timely dissipated. Therefore, a new type substrate made of Si is developed. Such a Si substrate has a heat conductivity larger than that of the sapphire substrate so that the heat generated by the layers can be effectively removed.
Nevertheless, the coefficient of thermal expansion (CTE) of the Si substrate does not well match with that of the layers. Thus, during operation of the LED chip, the Si substrate has a deformation different from that of the layers, resulting in a thermal stress concentrated at an interface between the substrate and the layers. Such concentrated thermal stress may cause fracture of the layers or even damage of the LED chip.
What is needed, therefore, is a semiconductor light-emitting structure which can overcome the limitations described above.